Quoting Chris Wilson (2019-10-03 14:19:46)

Make dma_fence_enable_sw_signaling() behave like its dma_fence_add_callback() and dma_fence_default_wait() counterparts and perform the test to enable signaling under the fence->lock, along with the action to do so. This ensure that should an implementation be trying to flush the cb_list (by signaling) on retirement before freeing the fence, it can do so in a race-free manner.

See also 0fc89b6802ba ("dma-fence: Simply wrap dma_fence_signal_locked with dma_fence_signal").

v2: Refactor all 3 enable_signaling paths to use a common function.

Signed-off-by: Chris Wilson chris@chris-wilson.co.uk

drivers/dma-buf/dma-fence.c | 78 +++++++++++++++++-------------------- 1 file changed, 35 insertions(+), 43 deletions(-)

diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c index 2c136aee3e79..4a1442a93f04 100644 --- a/drivers/dma-buf/dma-fence.c +++ b/drivers/dma-buf/dma-fence.c @@ -273,6 +273,30 @@ void dma_fence_free(struct dma_fence *fence) } EXPORT_SYMBOL(dma_fence_free);

+static bool __dma_fence_enable_signaling(struct dma_fence *fence) +{

•   bool was_set;
  

•   lockdep_assert_held(fence->lock);
  

•   was_set = test_and_set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
  

•                              &fence->flags);
  

•   if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
  

•           return true;
  

Perhaps this should be false for "could not _enable_ signaling as it was already signaled", which is closer to the original.

•   if (!was_set && fence->ops->enable_signaling) {
  

•           if (!fence->ops->enable_signaling(fence)) {
  

•                   dma_fence_signal_locked(fence);
  

•                   return true;
  

•           }
  

•           trace_dma_fence_enable_signal(fence);
  

•   }
  

•   return false;
  

+}

/**

• dma_fence_enable_sw_signaling - enable signaling on fence
• @fence: the fence to enable

@@ -285,19 +309,12 @@ void dma_fence_enable_sw_signaling(struct dma_fence *fence) { unsigned long flags;

•   if (!test_and_set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
  

•                         &fence->flags) &&
  

•       !test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags) &&
  

•       fence->ops->enable_signaling) {
  

•           trace_dma_fence_enable_signal(fence);
  

•           spin_lock_irqsave(fence->lock, flags);
  

•           if (!fence->ops->enable_signaling(fence))
  

•                   dma_fence_signal_locked(fence);
  

•   if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
  

•           return;
  
  

•           spin_unlock_irqrestore(fence->lock, flags);
  

•   }
  

•   spin_lock_irqsave(fence->lock, flags);
  

•   __dma_fence_enable_signaling(fence);
  

•   spin_unlock_irqrestore(fence->lock, flags);
  

} EXPORT_SYMBOL(dma_fence_enable_sw_signaling);

@@ -331,7 +348,6 @@ int dma_fence_add_callback(struct dma_fence *fence, struct dma_fence_cb *cb, { unsigned long flags; int ret = 0;

•   bool was_set;
  
    if (WARN_ON(!fence || !func))
            return -EINVAL;
  

@@ -343,25 +359,14 @@ int dma_fence_add_callback(struct dma_fence *fence, struct dma_fence_cb *cb,

    spin_lock_irqsave(fence->lock, flags);

•   was_set = test_and_set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
  

•                              &fence->flags);
  

•   if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
  

•   if (__dma_fence_enable_signaling(fence)) {
  

•           INIT_LIST_HEAD(&cb->node);
            ret = -ENOENT;
  

•   else if (!was_set && fence->ops->enable_signaling) {
  

•           trace_dma_fence_enable_signal(fence);
  

•           if (!fence->ops->enable_signaling(fence)) {
  

•                   dma_fence_signal_locked(fence);
  

•                   ret = -ENOENT;
  

•           }
  

•   }
  

•   if (!ret) {
  

•   } else {
            cb->func = func;
            list_add_tail(&cb->node, &fence->cb_list);
  

•   } else
  

•           INIT_LIST_HEAD(&cb->node);
  

•   }
  

•   spin_unlock_irqrestore(fence->lock, flags);
  
    return ret;
  

@@ -461,7 +466,6 @@ dma_fence_default_wait(struct dma_fence *fence, bool intr, signed long timeout) struct default_wait_cb cb; unsigned long flags; signed long ret = timeout ? timeout : 1;

•   bool was_set;
  
    if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
            return ret;
  

@@ -473,21 +477,9 @@ dma_fence_default_wait(struct dma_fence *fence, bool intr, signed long timeout) goto out; }

•   was_set = test_and_set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
  

•                              &fence->flags);
  

•   if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
  

•   if (__dma_fence_enable_signaling(fence))
            goto out;
  
  

•   if (!was_set && fence->ops->enable_signaling) {
  

•           trace_dma_fence_enable_signal(fence);
  

•           if (!fence->ops->enable_signaling(fence)) {
  

•                   dma_fence_signal_locked(fence);
  

•                   goto out;
  

•           }
  

•   }
  

•   if (!timeout) {
            ret = 0;
            goto out;
  

-- 2.23.0